1. Field of the Invention
The present general inventive concept relates to an image forming apparatus, and more particularly to a fusing device and an image forming apparatus having the same that fuses a toner image to a printing medium.
2. Description of the Related Art
An image forming apparatus is an apparatus that prints an image on a printing medium, e.g., paper, according to an input image signal. As one type of the image forming apparatus, an electrophotographic image forming apparatus is configured such that light is scanned to a photosensitive body which has been charged with a predetermined electric potential to form an electrostatic latent image on an outer peripheral surface of the photosensitive body. The electrostatic latent image is developed into a toner image by supplying a toner to the electrostatic latent image, and than the toner image is transferred onto paper. The toner image transferred onto the paper is just carried on the paper at this point, and is not fixed to the paper. Thus, the toner image necessarily passes through a fusing device provided in the image forming apparatus to be fused to the paper by heat and pressure.
A conventional fusing device includes a heat roller which has a heat source therein, and a press roller which is in close contact with the heat roller and forms a fusing nip at a contact portion with the heat roller. If the paper, onto which the toner image has been transferred, passes between the rotating heat roller and press roller, the toner image is fused to the paper by heat transferred from the interior of the heat roller and pressure generated at the fusing nip. However, in the conventional fusing device, because the heat roller itself has a large thermal capacity, it takes much time to heat the heat roller to a predetermined temperature, at which the fusing can be achieved, in initially driving the image forming apparatus.
In order to fulfill the requirements of high speed operation of the image forming apparatus, there has been recently developed a fusing device capable of increasing a temperature of a nip portion to a temperature for image fusing, as quickly as possible. An example of such a fusing device is disclosed in Korean Patent Laid-Open Publication No. 2006-0090740.
The disclosed fusing device includes a press roller, a fusing belt which rotates by being driven by the press roller, a halogen heater mounted in the interior of the fusing belt to heat the fusing belt, and a belt guide member supporting an inner surface of the fusing belt so that the fusing belt can form a fusing nip together with the press roller. In the above-structured fusing device, the heat emitted from the halogen heater heats the belt guide member, and the belt guide member transfers the heat to the fusing belt to heat the fusing belt.
The disclosed conventional fusing device can only shorten a warm-up time to a certain extent by using the fusing belt having a relatively small thermal capacity. However, because the heat is indirectly transferred to the fusing belt through the belt guide member, there is a limitation in increasing rapidly the temperature of the fusing belt.
Also, the disclosed conventional fusing device is designed without consideration of the deformation of the belt guide member forming the fusing nip due to the heat of a high temperature. Thus, it is highly possible that a width of the nip portion becomes narrow or the temperature of the fusing belt drops due to the thermal deformation of the belt guide member (if a contact area between the belt guide member and the fusing belt decreases due to the thermal deformation, the quantity of heat transferred to the fusing belt also decreases, and thus the temperature of the fusing belt drops). The decrease in the width of the nip portion or the drop of the temperature of the fusing belt causes deterioration of the fusing performance, and as a result deterioration of a printing quality or image inferiority occurs.